The study of hydrocarbon fluorescence for the purpose of downhole formation fluid evaluation using a wireline logging tool has been proposed in numerous patents (e.g. U.S. Pat. Nos. 2,206,922; 2,346,481; 2,334,475; 6,140,637; and 6,268,603, each of which is incorporated by this reference). As described in one or more of the patents identified above, the proposed methods are generally directed to moving a wireline logging tool through a borehole while irradiating the formation. The methods teach detecting fluorescence through an optically transparent material, which is pressed against the borehole wall. However, in order to be useful to any degree, the transparent material must be pressed against the borehole wall with sufficient force to displace the mud cake. Unfortunately, the natural fluorescence of certain shale and hydrocarbon bearing rocks complicates the interpretation of the logs and the methods taught by the prior art have not been widely adopted.
Schlumberger's Modular Formation Dynamics Tester (MDT™) collects multiple samples at any number of stations in a well. Formation fluids are hydraulically isolated from the drilling fluids (and the mud cake) in the well. The formation fluid is drawn into a flow line inside the MDT tool body and analyzed using absorption spectroscopy through a sapphire optical cell. Contamination monitoring tells the operator when to capture a sample. GOR (Gas/Oil Ratio—the ratio of produced gas to produced oil) and compositional information can be determined by the LFA™ tool and CFA™ tool respectively. However, because the number of available sample bottles contained by the MDT is limited, some have proposed a quasi-continuous log of the formation fluids that could be generated without sample collection. Taking a quasi-continuous log without sample collection is generally referred to as “gargling”. Gargling methods are discussed in U.S. Pat. Nos. 6,476,384; 6,465,775; 5,859,430; and 5,939,717, each of which is incorporated by this reference.